U.S. Pat. No. 3,636,132 issued Jan. 18, 1972 to Saegusa, et al., the teachings of which are incorporated by reference, describes the synthesis of ABA block copolymers produced by sequential polymerization of substituted oxetanes and THF's. By selection of A blocks which are crystalline at ambient temperatures and B blocks which are amorphous at room temperature, block polymers are produced which exhibit thermoplastic characteristics. This patent notes that homopolymers of 4 and 5 member ring cyclic ethers tend to be crystalline and copolymers tend to be amorphous at ambient temperatures. However, it is known that some homopolymer blocks may be amorphous at ambient temperatures.
U.S. Pat. No. 4,393,199 issued July 12, 1983 to Manser, the teachings of which are incorporated herein by reference, describes cationic polymerization of cyclic ethers using a polyol initiator and an acid catalyst. This patent teaches that a ratio cf diol to a Lewis Acid, i.e., the ratio of butanediol to BF.sub.3 initiator species, should be about 1:2, which is about 1 mole of BF.sub.3 for each mole of hydroxyl groups. In Example 6, U.S. Pat. No. 4,393,199 teaches that no polymerization occurs if the ratio of butanediol to BF.sub.3 is 1:1.
U.S. Pat. No. 4,483,978 issued Nov. 20, 1984 to Manser, the teachings of which are incorporated by reference, is directed to copolymerization of 4 and 5 member ring cyclic ethers.
U.S. Pat. No. 4,806,613 issued Feb. 21, 1989 to Wardle, the teachings of which are incorporated herein by reference, notes deficiencies with known sequential cationic polymerization methods for obtaining thermoplastic elastomeric characteristics from 4 and 5 member ring cyclic ethers. Because such block polymers which exhibit thermoplastic elastomers have significant potential for use as binders in high-energy compositions, such as explosives, propellants, gasifiers and the like, this patent takes a different approach to producing thermoplastic block polymers. This patent proposes separately synthesizing crystalline A blocks and amorphous B blocks and then linking the A and B blocks. Although the method taught in this patent has produced thermoplastic, elastomeric block polymers having good characteristics especially suitable for binder use in high-energy compositions, the linking method taught therein is a multi-step procedure which results in a higher cost in producing the desired block polymers. As large quantities of thermoplastic elastomer may be required, for example, to serve as a propellant binder in a large rocket motor, new methods of synthesizing thermoplastic, elastomeric block polymers from cyclic ethers is desirable.